The present invention relates to an overlay concrete for overlaying existing concrete fabrics to repair or remodel the fabrics, and a bonded overlay rehabilitation method using the overlay concrete. The present invention relates in particular to a bonded overlay rehabilitation method using an overlay concrete suitable for the use in a bonded overlay rehabilitation method or the like which is performed in repair work of concrete fabrics, in particular, concrete pavements of a runway, a road or the like.
Recently, in repair work of existing concrete fabrics having a surface layer strength lowered by cracks or crevices based on an increase in the wheel load, or exposure of aggregates, for example, in repair work of fabrics such as a paved runway or road, a so-called bonded overlay rehabilitation method has been adopted. In the bonded overlay rehabilitation method, the surface of the existing concrete fabrics is overlaid with a new concrete to form a concrete layer having a given thickness on the existing concrete fabrics.
Hitherto, therefore, various investigations have been made to improve bond strength in the joint interface.
For example, Japanese Patent Application Laid-Open No. 9-71902 discloses a bonded overlay rehabilitation method of jetting highly-pressured water on the surface of an existing concrete by water jet to form macro-texture, jetting a large number of small and hard balls composed of a metal such as iron onto the macro-texture by shot blast to form micro-texture, and overlaying the surface of the existing concrete, which has the macro-texture and the micro-texture, with a new concrete to form a concrete layer having a given thickness on the surface of the existing concrete.
According to this bonded overlay rehabilitation method, the surface of the existing concrete, which will be a joint interface, has numerous macro-texture and micro-texture; therefore, the new concrete for the overlay is inserted in a wedge manner into the texture so that the bond strength in the joint interface can greatly be improved. Further, the macro-texture and the micro-texture at the surface of the existing concrete are formed by combination of water jet and shot blasting and, therefore, the formation of the texture at the surface of the existing concrete is easy and prompt and does not make the strength of the surface layer thereof weak. Thus, the bonded overlay rehabilitation method has advantages such as remarkable shortening of construction period.
However, the above-mentioned publication never discloses properties which the new concrete for overlaying the surface of the existing concrete be should have in order to repair or remodel it (The new concrete will be referred to as an xe2x80x9coverlay concretexe2x80x9d). As to what properties the overlay concrete should have in order to raise the bond strength optimally, therefore, there has remained a room for investigation.
For example, even if texture is formed at the surface of an existing concrete to improve bond in the case that the flowability of the overlay concrete is low, filling performance of the concrete into the texture is bad. Thus, it appears that the bond strength of the joint interface cannot be improved. On the other hand, in the case that the used overlay concrete contains a large amount of water to increase its flowability, delamination (separation) or stress arises in the joint interface, resulting from drying shrinkage at the time of hardening of the concrete. Thus, it appears that the bond strength in the joint interface deteriorates. Scraps generated at the time of forming the texture, dust from the outdoors, and the like are present on the surface of the existing concrete fabrics. Thus, it appears that the bond is deteriorated by these scraps.
From these viewpoints, special properties of flowability, drying shrinkge, involvement performance of the scraps and the like, which are different from those of usual concrete, are required for the overlay concrete in order to raise the bond strength to the existing concrete surface.
In the light of the speciality of the properties required for an overlay concrete for overlaying existing concrete fabrics in order to repair or remodel the fabrics by the above-mentioned bonded overlay rehabilitation method or the like, an object of the present invention is to provide an overlay concrete which is good in bond to the surfaces of the existing concrete fabrics; and which satisfies properties required for usual concrete, such as strength, durability and workability. Another object of the present invention is to provide such an overlay concrete that, when being applied to a concrete pavement, its formed surface itself can become a pavement surface, and to provide a bonded overlay rehabilitation method using the above-mentioned overlay concrete.
The inventors have been making tests and investigations to attain the above-mentioned objects. As a result, the inventors have found that a concrete having a specific mix proportion becomes an overlay concrete which can attain the above-mentioned objects, that is, which is good in bond to the surface of existing concrete fabrics and can satisfy properties such as strength, durability and workability. Thus, the present invention has been made.
That is, the present invention is an overlay concrete comprising an AE water reducing agent or superplastisizer, and having a slump of 2 to 8 cm, a cement-water ratio of 35 to 45%, and a sand-coarse aggregate ratio of 36 to 42%.
The overlay concrete having this mix proportion is good in filling performance into texture present at the surface of existing concrete fabrics and the involvement performance of scraps. The present overlay concrete also has small drying shrinkage, so that less delamination or stress arises at a joint interface. Thus, a new concrete layer having a high bond strength can be formed on the existing concrete fabrics.
Preferably, the overlay concrete further comprises an organic shrinkage reducing agent.
If the concrete comprises the organic shrinkage reducing agent, the amount of drying shrinkage when the concrete is hardened is further reduced so that less cracks arise. The generation of delamination or the stress at the joint interface is further suppressed. Advantageously, therefore, the bond strength to existing stress fabrics becomes higher.
In order to overlay existing concrete fabrics with the overlay concrete according to the present invention, it is preferred to jet highly-pressured water on the surface of an existing concrete fabric by water jet to form macro-texture, jet small and hard balls composed of a metal such as iron onto the macro-texture by shot blast to form micro-texture, and overlay the surface of the existing concrete with the overlay concrete, with vibration, as disclosed in Japanese Patent Application Laid-Open No. 9-71902.
According to this bonded overlay rehabilitation method, it is possible to form easily and promptly numerous macro-texture and micro-texture, into which the overlay concrete of the present invention will be inserted in a wedge manner, without making the strength of the surface layer of the existing concrete weak. Therefore, it is possible to make the best use of the properties of the overlay concrete of the present invention, such as high filling performance into the texture, high involvement performance of scraps, and low drying shrinkage when the concrete is hardened, and form the new concrete layer having a high bond strength at the joint interface on existing concrete fabrics for a short time.
Concerning the vibration applied when the surface of an existing concrete having macro- and micro-texture is overlaid with the overlay concrete of the present invention, the frequency of the vibration is preferably from 2600 to 3700 vpm, and the time for applying the vibration is preferably from 10 to 60 seconds.
If the frequency of the vibration and the time for applying the vibration are out of the above-mentioned ranges, the overlay concrete of the present invention is not sufficiently compacted. Moreover, the involvement performance of scraps deteriorates.
The overlay concrete of the present invention is a concrete having a slump of 2-8 cm; a flexural strength, after hardening of the concrete, of 57 kgf/cm2 or more; and a compressive strength of about 500 kgf/cm2. Concrete fabrics having such properties can be naturally applied to use besides concrete pavements. Various panels, coatings, or the like can be applied onto the overlay concrete.